/Engine/Plugins/Runtime/CommonUI/Source/CommonUI/Public/Widgets/CommonActivatableWidgetContainer.h
Generates (either creates or pulls from the inactive pool) instance of the given widget class and adds it to the container. The provided lambda is called after the instance has been generated and before it is actually added to the container. So if you've got setup to do on the instance before it potentially activates, the lambda is the place to do it.
template<typename ActivatableWidgetT> ActivatableWidgetT * AddWidget ( [TSubclassOf](API\Runtime\CoreUObject\Templates\TSubclassOf)< [UCommonActivatableWidget](API\Plugins\CommonUI\UCommonActivatableWidget) > ActivatableWidgetClass, [TFunctionRef](API\Runtime\Core\GenericPlatform\TFunctionRef)< void(ActivatableWidgetT &)> InstanceInitFunc )